This invention is directed to radiography. In particular, it is directed to a radiographic silver halide film that provides medical diagnostic images of soft tissues such as in mammography and exhibits reduced dye stain.
The use of radiation-sensitive silver halide emulsions for medical diagnostic imaging can be traced to Roentgen""s discovery of X-radiation by the inadvertent exposure of a silver halide film. Eastman Kodak Company then introduced its first product specifically that was intended to be exposed by X-radiation in 1913.
In conventional medical diagnostic imaging the object is to obtain an image of a patient""s internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) and U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Kelly et al.), U.S. Pat. No. 4,900,652 (Kelly et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and Research Disclosure, Vol. 184, August 1979, Item 18431.
While the necessity of limiting patient exposure to high levels of X-radiation was quickly appreciated, the question of patient exposure to even low levels of X-radiation emerged gradually. The separate development of soft tissue radiography, which requires much lower levels of X-radiation, can be illustrated by mammography. The first intensifying screen-film combination (imaging assembly) for mammography was introduced to the public in the early 1970""s. Mammography film generally contains a single silver halide emulsion layer and is exposed by a single intensifying screen, usually interposed between the film and the source of X-radiation. Mammography utilizes low energy X-radiation, that is radiation that is predominantly of an energy level less than 40 keV.
U.S. Pat. No. 6,033,840 (Dickerson) and U.S. Pat. No. 6,037,112 (Dickerson) describe asymmetric imaging elements and processing methods for imaging soft tissue.
Problem to be Solved
In mammography, as in many forms of soft tissue radiography, pathological features that are to be identified are often quite small and not much different in density than surrounding healthy tissue. Thus, differences in X-radiation attenuation between normal and diseased soft tissue are very small. Film artifacts and other distracting film features can sometimes interfere with the difficult task of seeing these small differences. Thus, mammography is a very difficult task in medical radiography. Small distractions, such as dye stain, reduce the ability of the user to detect these small differences. As a result, there is a continuing desire to improve the image quality of mammography films, and particularly to reduce dye stain and to increase contrast.
This invention provides a solution to the noted problems with a radiographic silver halide film that comprises a support having first and second major surfaces and that is capable of transmitting X-radiation,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer,
at least one of the silver halide emulsion layers comprising cubic silver halide grains that have the same or different composition,
at least one of the cubic grain silver halide emulsion layers comprising a combination of first and the second spectral sensitizing dyes that provides a combined maximum J-aggregate absorption on the cubic silver halide grains of from about 540 to about 560 nm, and
wherein the first spectral sensitizing dye is an anionic benzimidazole-benzoxazole carbocyanine, the second spectral sensitizing dye is an anionic oxycarbocyanine, and the first and second spectral sensitizing dyes are present in a molar ratio of from about 0.25:1 to about 4:1.
Further, this invention provides a method of providing a black-and-white image comprising exposing a radiographic silver halide film of this invention and processing it, sequentially, with a black-and-white developing composition and a fixing composition, the processing being carried out within 90 seconds, dry-to-dry.
A radiographic imaging assembly of the present invention comprises a radiographic film of this invention that is arranged in association with a fluorescent intensifying screen.
The present invention provides a means for providing radiographic images for mammography exhibiting improved image quality by reducing dye stain while increasing contrast. In addition, all other desirable sensitometric properties are maintained and the radiographic film can be rapidly processed in the same conventional processing equipment and compositions.
These advantages are achieved by using a novel combination of two different spectral sensitizing dyes that exhibit a combined J-aggregate xcexmax of from about 540 to about 560 nm when absorbed to the cubic silver halide grains in at least one of the silver halide emulsion layers.